Digital clock

ABSTRACT

A digital clock is provided which includes a main shaft rotatably supporting a plurality of time indicating drums which have inner teeth on one side and driving teeth on the other side of their inner periphery. The clock also includes pinion locking means arranged within the time indicating drums on the same side as said driving teeth. A plurality of intermediate pinions are arranged within the drums to engage the pinion locking means and driving teeth on one side and with the inner teeth on the other side so that said drums are driven. One or two of the pinions consist of two parts which are slippable relative to each other by application of a predetermined torque therebetween for the purpose of time adjustment or day of week indication adjustment. A time mechanism installed in the clock includes a cam drum which is within a time setting drum.

0 United States Patent 1 1 [H1 3,903,685

Goto Sept. 9, 1975 DIGITAL CLOCK Primary ExaminerJoseph W. Hartary Assistant ExaminerU. Weldon 75 l t K G t T k .l 1 nven or emu-o o 0 yo apan Attorney, Agent, or FirmArmstrong, Nikaido 8L [73] Assignee: Mansei Kogyo Kabushiki Kaisha, Wagner Japan 221 Filed: July 1, 1974 57 ABSTRACT [21 Appl. No.: 484,867 A digital clock is provided which includes a main shaft rotatably supporting a plurality of time indicating Related Apphcatlon Data drums which have inner teeth on one side and driving [62] of 409,469* 1973' teeth on the other side of their inner periphery. The clock also includes pinion locking means arranged [30] Fol-mg Apphcamm Pnorny Dam within the time indicating drums on the same side as Nov. 9, 1972 Japan 47-l29308[U] said driving teeth. A plurality of intermediate pinions are arranged within the drums to engage the pinion 58/|25 2 E locking means and driving teeth on one side and with [51 Int. Cl. G04B 13/00 th inner teeth on the other side so that said drums are l Field Search 58/125 126 l9 driven. One or two of the pinions consist of two parts 16 235/1 1 17 R which are slippable relative to each other by application of a predetermined torque therebetween for the [56] References Cited purpose of time adjustment or day of week indication UNITED STATES PATENTS adjustment. A time mechanism installed in the clock 2459 107 1/1949 Johnson 58/126 E includes a cam drum which is within a time 2,539,138 1/1951 Johnson .1 58/19 R drum- 3,636,699 l/l972 Marble 58/l25 C l3 Claims 11 Drawing Figures 1 1 5 I J I II I II I l lb O 1 1L1 l 1oo\ f f 1 20v- 1 05 J 1 0 PATEHTED 95975 3,903,685

SHEET 1 [IF 3 1 1+ 4 25 51 50 22 be A 20 FIG. 1

PRIOR ART 2 PATENTEU 3,903,685

SHEET 2 BF 3 110 15 FIG. 5

PATENTEU P 3, 903,685

SHEET 3 BF 3 FIG. 8 FIG. 7

FIG. 9 109 PRIOR ART 1o1- DIGITAL CLOCK This is a division of application Ser. No. 409,469 Filed Oct. 25, 1973.

BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to an improved digital clock mechanism including a timer for operating a switch, and an alarm 2. Description of the Prior Art Heretofore. a clock mechanism has been disclosed wherein a plurality of time indicating drums are mounted on a main shaft so that the drums may be driven intermittently through a double-profile pinion which is mounted on an another shaft outside of the time indicating drums (US. Pat. No. 3,495,396). However, in such a mechanism, mounting space required for the pinion and its shaft causes bulkiness of the clock and pinion clearing gap between the adjacent time indicating drums, especially between the ten minute indicating drum and the unit minute indicating drum. resulting in difficulty in reading time.

Further, in a conventional digital clock, a time adjusting mechanism comprises a particular clutch means arranged between a driving motor and a time indicating drum or between adjacent time indicating drums (US. Pat. No. $690,063). It has been found, however, that such a clutch means involves a complicated structure. The structure is especially difficult to make using injection molding for the time indicating drums of synthetic resin due to their complicated shape which is caused by the clutch means and a pinion gear disposed inside of the time indicating drums.

A conventional timer device used in a digital clock comprises a cam disk provided with outer teeth for mating with a pinion gear which is driven in unison with the time indicating drums. At least one lug is formed on the cam disk. and at least one cut out portion is formed on time setting wheel whereby a timer switch is so arranged that the switch is operated when the lug on the cam disk enters into the corresponding cut out portion on the time setting wheel. However, such a timer construction requires not only considerable space in a digital clock but also relatively complicated assembling process.

Further, in a conventional digital clock, a driving motor generally drives directly a second indicating drum or a unit minute indicating drum which is disposed at right-hand side in a succession of time indicating drumsv Therefore. a time adjusting wheel and/or a timer adjusting wheel are conventionally disposed separately from each other resulting in difficulty in operation or complicated structure of the clock.

SUMMARY OF THE INVENTION Accordingly. one of the features of the present invention is to provide an improved digital clock mechanism comprising a plurality of time indicating drums having inner peripheral teeth the driving torque for which is transmitted through double-profile pinions arranged inside of the time indicating drums. The pinions are carried on shafts fixed on plate members which are interposed between the adjacent time indicating drums to be carried on a main shaft. Such pinions may selectively comprise two parts which are resiliently coupled with each other but slippable relative to each other by application of a predetermined torque for the purpose of time adjustment or day of week indication adjustment.

Still another feature of the present invention is to provide an improved timer mechanism for use in a digital clock, comprising a time setting drum carried on a shaft, a cam drum positioned within the time setting drum carried on said shaft, inner teeth formed on the inner periphery of the cam drum, the inner teeth mated with a pinion which is driven through an idler gear by a driving shaft, 21 lug arranged on the cam drum, and a cut out portion arranged on the time setting drum, whereby a switch means is operated when the lug enters into the cut out portion.

Still another feature of the present invention is to provide an easily handled adjusting mechanism for time indication and a timer setting in a digital clock wherein time indicating drums are carried rotatable around a main shaft. A time setting drum for a timer is fixed on the left end of the main shaft and a timer adjusting wheel is fixed to the right end. The unit minute indicating drum is fixed on the left end of a hollow outer shaft through which the main shaft extends and a time ad justing wheel is fixed on the right end of the outer shaft adjacent to the timer adjusting wheel. Thus the two adjusting wheels are arranged adjacent to each other at the right side of the clock.

Accordingly, it is a general object of the present invention to provide an improved digital clock mechanism overcoming aforementioned difficulties in conventional digital clocks.

More specifically. it is an object of the present invention to provide an improved driving mechanism in a digital clock to drive a succession of the time indicating drums.

It is another object of the present invention to pro vide an improved adjusting mechanism for time indication in a digital clock.

It is still another object of the present invention to provide an improved quick changer mechanism for day of week indication in a digital clock.

It is still another object of the present invention to provide an improved adjusting mechanism of easy adjusting of the time indication and timer setting in a digital clock.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects. features and advantages of the present invention will be apparent from the following description of preferred embodiment of the invention taken in connection with the accompanying drawings forming a part thereof in which:

FIG. I is a fragmentary view partly in section showing a conventional driving mechanism in a digital clock.

FIG. 2 is an axial sectional view showing the improved driving mechanism and time adjusting mechanism of the invention.

FIG. 3 is an exploded perspective view showing a pair of adjacent time indicating drums in FIG. 2.

FIG. 4 is a front elevation partly in section showing an improved arrangement of adjusting wheels for time indication and timer setting.

FIG. 5 is an enlarged sectional view showing a pinion in a modified embodiment according to the invention.

FIG. 6 is an enlarged sectional view showing a pinion of another embodiment.

FIG. 7 is an enlarged sectional view showing a pinion of still another embodiment.

FIG. 8 is an enlarged left side elevation in FIG. 7.

FIG. 9 is a fragmentary sectional view showing a conventional timer mechanism for a digital clock.

FIG. 10 is a fragmentary sectional view showing an improved timer mechanism in a digital clock according to the present invention.

FIG. 11 is a perspective view broken in part showing the timer mechanism in FIG. 10 mounted in a digital clock.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to FIG. I, there is shown a conventional driving mechanism in a digital clock, wherein a lower order time indicating drum 1 and an upper order time indicating drum 2 are mounted rotatably around a common main shaft 3 passing therethrough. A douhie-profile pinion 4 rotatably supported on a pinion shaft 5 which is arranged outside of the time indicating drums l and 2 is adapted to mate with outer driving teeth or lugs 6 on the lower order drum 1 and with outer peripheral teeth 9 on the upper order drum 2 so that driving torque may be transmitted intermittently through the pinion 4 between the adjacent drums.

Referring to FIGS. 2 and 3, there is shown an improved clock mechanism according to the present invention. wherein a second time indicating drum ll is numbered on the outer periphery thereof from to with five graduations therebetween, a unit minute indicating drum 12 is numbered on its outer periphery from "0" to "9", a ten minute indicating drum [3 is numbered on its outer periphery in two repeating series of numbers from 0" to 5", an hour indicating drum 14 is numbered on its outer periphery from I to l2, and a day of week indicating drum 15 is numbered on its outer periphery from SUN.AM to SAT.PM". A main shaft 10 extends through a pair of opposing walls of frame and rotatably supports thereon the second drum 11, the unit minute drum 12, the minute drum l3, and the hour drum [4 and the day of week drum 15. Between adjacent drums circular support plates l6, 17, 18 and 19 are interposed and are piered by the main shaft 10 and which support doubleprofile pinions 21, 22, 23, 24, and 26 respectively thereon in such a manner that the pinions are arranged inside of the time indicating drums. The outer configuration of the support plates l6, l7, l8 and 19 are generally flush with the adjacent time indicating drums, but some lugs (not shown) may be formed on the support plates for fixation onto frame 20.

An electric motor 27 is fixed on the frame 20 adjacently to the second drum 1] for supplying a driving torque to the second drum ll. A pinion 29 carried on a driving shaft 28 of the motor 27 extends through the wall of the frame 20 to mate with inner teeth 31 formed on the inner face of a concentrically projecting wall 30 on the right side of the second drum I]. The teeth 31 mate with the pinion 29 on the motor and may be formed on the outer side periphery of the second drum ll because of the location of the motor and its driving shaft. On the inner periphery at the left side of the second drum 11, there is provided a pair of driving teeth and a pinion locking face 32.

The relation between the driving teeth, a pinion locking face and a double-profile pinion is described in connection with the unit minute drum 12, ten minute drum [3 and double-profile pinion 23 as illustrated in FIG. 3. On the inner periphery at the left side of the unit minute drum 12 there is provided a pair of driving teeth 40 and 41 and a pinion locking face 33 which is a little shorter in the axial direction of the drum 12 than the driving teeth 40 and 41. The support plate 17 has an eccentric recess 42. A shaft 43 rotatably carrying the double-profile pinion 23 passes through. This pinion is of the same type as a known double-profile pinion for use in a digital counter and constructed such that the left-hand side thereof is nine-toothed, whereby the three teeth on the left-hand side of the pinion 23 extend to form the three teeth on the rightl-hand-side thereof and the remaining teeth of the left-hand-side are not extended. The pinion 23 is arranged on the shaft 43 in such a manner that the three-toothed side thereof protrudes through a cut out portion 44 of the recess 42 on the support plate 17 such that the three-toothed side mates with the driving teeth 40 and 41 and the pinion locking face 33 on the unit minute drum 12, wherein the six teeth on the pinion 23 are short enough not to reach the locking face 33 but long enough to engage the pair of driving teeth 40 and 41 for smooth driving of the pinion 23 by the driving teeth. The nine-toothed side of the pinion 23 is adapted to engage the 36- toothed inner periphery 37 of the ten minute drum 13.

In operation, one revoultion of the unit minute drum 12 causes the pair of driving teeth 40 and 4] thereon to advance only the three teeth on the left-hand side of the double-profile pinion 23, and thereafter, the pinion locking face 33 of the drum 12 steps the rotating movement of the pinion 23 at its three-toothed side until the pair of driving teeth 40 and 41 mate again with the three-toothed side. Therefore one revolution of the unit minute drum 12 causes 1/12 of a revolution of the ten minute drum 13.

In the substantially same manner as mentioned above. the pair of driving teeth (not shown) and pinion locking face 32 on the second drum 11 are adapted to mate with the right-hand side 21 of the double-proiile pinion 21 and 22, the left-hand side of which engages with 30-toothed inner periphery 36 of unit minute drum 12. The pinion 21 and 22 is rotatably carried on a shaft 45 on the support plate 16 and comprises two parts 21 and 22 as described hereinafter. Diametrically opposed two pairs of driving teeth (not shown) and two pinion locking faces 34 on the left-hand side of the ten minute drum 13 are adapted to mate with the righthand side of the double-profile pinion 24, the left-hand side of which engages with 36-toothed inner periphery 38 of the hour drum 14. The pinion 24 is rotatably carried on a shaft 46 on the support plate 18. A pair of driving teeth (not shown) and a pinion locking face 35 on the left-hand side of the hour drum 14 are adapted to mate with the right-hand side 25 of the doubleprofile pinion 25 and 26 the left-hand side of which engages with a 42 toothed inner periphery 39 of the day of week drum is. The pinion 25 and 26 is rotatably carried on a shaft 47 on the support plate 19 and comprises two parts 25 and 26 as described below. All of the double-profile pinions 21, 22, 23, 24, 25 and 26 are three-toothed on the right-hand side and nine-toothed on the left-hand side. The support plate 16 or 18 between the drum I] and unit minute drum 12 or between the ten minute drum l3 and hour drum [4 is formed thicker than the other support plates 17 and I9 so that adjacent drums l1 and 12 or 13 and 14 may be clearly separated in location for easy reading of the time. For the same purpose, a colon mark (see FIG. 11) may be impressed on the support plate 18. Further, a neon lamp (not shown) may be installed at the inner hollow of the support plate 18 and/or 16 for illuminating the time indicating drums from the inside when the drums are made of translucent or transparent material such as synthetic resin.

Thus one revolution of the second drum 11 causes l/ revolution of the unit minute drum 12, one revolution of which causes l/12 revolution of the ten minute drum 13 as already described, one revolution of which causes l/12 revolution of the hour drum 14, one revolution of which causes l/14 revolution of the day of week drum l5, and as a result, each drum digitally indicates minutes, hours and clay of week.

The double-profile pinion 21 and 22 between the second drum 11 and the unit minute drum 12 comprises two parts 21 and 22. One part 21 is provided with at least one and at the most three projections 48 on its side end facing the part 22 while the other part 22 is provided with three recesses 49 on its side end facing the part 21 such that the recesses 49 may receive the projections 48. The two parts 21 and 22 are so arranged on the shaft 45 that the part 22 is biased toward the part 21 by a coil spring 50 around the shaft 45, one end of which abuts against a washer-like retainer 51 fixed on the shaft 45 and the other end of which pushes the part 22. These two parts are thus pressed against each other in engaged driving but slippable relation. The part 22 is formed with a central recess to partially accommodate the spring 50. The bushing 52 of the unit minute drum 12 is detachably fixed on an end of a first outer shaft 53 through wich the main shaft 10 rotatably extends. A time adjusting wheel 54 is fixed on the other end of the outer shaft 53 (see FIG. 4) to operate the unit minute drum 12.

In operation, the time adjusting wheel 54 rotates. through the first outer shaft 53, the unit minute drum 12 which is rotatable together with the left-hand part 22 of the double-profile pinion since the part 22 is rotatably slippable against the pressing force of the spring 50 relative to the part 21 which is stopped by the pinion locking face 32 on the second drum 1 1. Thus the indicated time is adjustable by revolution of the time adjusting wheel 54 which is transmitted incrementally to the unit minute drum 12, the ten minute drum 13, the hour drum I4, and finally the day of week drum 15.

FIG. 5 illustrates another embodiment of the doubleprofilc slippable pinion of the type described above, wherein a first part 59 is provided on one end facing a second part 60 with plural projections 61 and 62. A central bushing 63 is formed thereon with an enlarged head 64 and with one or more slits 65 such that the central bushing 63 may bear resiliency in the diametrical direction of the bushing which will permit the second part 60 to fit onto the central bushing 63 over the enlarged head 64. The central bushing 63 extends beyond the second part 60. The second part 60 may be slid when the double-profile slippable pinion is in operative condition. A coil spring 66 is positioned between the second part 60 and an E ring 67 supported on the head 64 of the central bushing 63 so that the second 6 part 60 is held against the first part 59 whereby recesses 68 and 69 on the second part, facing the first part 59, receive the corresponding projections 61 and 62.

FIG. 6 illustrates still another embodiment of the double-profile slippable pinion wherein a first part 70 is provided with a central bushing 71 on the outer end of which is formed plural circumferential recesses 72 and 73. The recesses 72 and 73 are adapted to receive corresponding projections 74 and 75 formed on plural resilient tongues 76 and 77 which extend from a second part 78 around the central bushing 71 of the first part 70. Thus the second part 78 is rotatable by application of a predetermined torque thereon relative to the first part 70 whereby the projection 75 on the resilient tongue 77 is positioned in the adjacent recess (not shown) on the central bushing 71. The central bushing 71 may be formed with an extension (not shown) beyond the resilient tongues 76 and 77 so that a washer- Iike retainer (not shown) may be fixed on the extension to prevent the second part 78 from disengaging the central bushing 71.

FIGS. 7 and 8 illustrate still another embodiment of the double-profile pinion wherein a first part 79 is provided with a central bushing 80 of square cross section which is received within a cylindrical inner space 81 of a second part 82. The circumferential face of the central bushing 80 abuts against an arcuated leaf spring 83 both ends of which are supported on step portions 84 and 85 on the inner periphery of the second part 82, to control the intermittent revolutions of the bushing 80. The second part 82 is rotatable by a predetermined torque relative to the first part 79 with the leaf spring 83 moving over the corner edges 86 of the central bushing 80.

The double-profile pinions shown in FIGS. 5 to 8 are as seen from the drawings, four-toothed on the right side and eight-toothed on the left side. It is to be unders stood that the number of teeth on each side of the pinion can be altered for the purpose of the present invention and within the scope of the invention. It is also advantageous to make the pinions of synthetic resin.

FIG. 9 shows a conventional timer mechanism for a digital clock, wherein a time setting drum 87 is rotatably carried on a shaft 86. The side face of the drum has one or more recesses or cut out portions 89 which are adapted to accommodate corresponding projections 90 and 91 formed on a side end of a cam disk 92 rotatably carried on the shaft 86 and arranged outside of the time setting drum 87. Circumferential gear 93 on the cam disk 92 mates with a pinion 94 driven by, for instance a drum such as the drum shown in FIG. 1 so that the cam disk 92 may be rotated to move the projections 90 and 91 thereon into the corresponding recesses 89 on the time setting drum 87. The cam disk 92 is thus pushed toward the time setting drum 87 by a plate 95 biased by spring 96. and thus a switch 97 is operated.

Referring to FIGS. 4, l0 & l l, a timer mechanism according to the present invention is shown wherein a time setting drum 98 is fixed on the main shaft 10. The drum 98 accommodates a cam drum 102 of smaller diameter in such a manner that the cam drum 102 is rotatable around a bushing 103 of the time setting drum 98. The drum 102 is biased axially toward the time setting drum 98 by a spring 104 interposed between the drum 102 and a washer-like retainer 105 fixed on the 5 outer end of the bushing 103. The cam drum 102 is 99 formed on the time setting drum 98. The time setting drum 98 is biased together with the cam drum 102 by a spring 120 disposed between the frame and the time setting drum 98 toward the time indicating drum so that the extreme end of the bushing 103 abuts the side face of a pinion 109 on the second outer shaft 110.

A reduction gear 107 is rotatably carried around a shaft 108 on the frame 20. The reduction gear comprises a pinion side l07b to gear with inner peripheral teeth 106 on the cam drum 102 and a wheel side 107::

to mate with the pinion 109 at one end of the second outer shaft 110 disposed around the main shaft 10. The pinion 109 is formed integrally on one end of the second outer shaft 110 to transmit the rotational movement of the ten minute drum 13. The ten minute drum 13 is indetachably fixed relation with the other end of the second outer shaft 110 (see FIG. 2 or 4).

A switch 111 such as a microswitch is arranged on the frame 20 to be operated by horizontal axial movement of the cam drum 102 around the bushing 103 of the time setting drum 98. The projections 100 and 101 on the cam drum 102 are adapted to separate the drum 102 from the time setting drum 98 in the inoperative position of the timer, and are so arranged at radially different positions on the side face of the cam 102 that the projections enter into the correspondingly disposed slots 99 on the time setting drum 98 only one time each revolution of the cam drum 102. Thus one complete revolution of the cam drum I02 causes one operation of the switch 111.

The time setting drum 98 is numbered at its outer periphery from l to l2 or 24 and is formed at the peripheral side portion with ratchet gears 113 mated with a spring biased pawl 114 carried around a shaft 115 on the frame 20. Thus the time setting drum 98 rests in the respective setting position and may be rotatable in one direction to protect other mechanisms in the digital clock. The time setting drum 98 is adjustable from the outside through the main shaft 10. The main shaft 10 fixedly supports on one end the time setting frum 98 and fixedly supports on the other end a timer adjusting wheel 112 adjacent to and outside of the time adjusting wheel 54 at the righthand side of the digital clocks as shown in FIG. 4.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraces therein.

What is claimed is:

l. A digital clock comprising:

a driving source;

a frame;

a main shaft supported on said frame;

a plurality of time indicating drums rotatably mounted on said main shaft for indicating the time;

a coupling means for forming an operative connection between said driving source and said time indicating drums and adapted to convey a driving force from said driving source to the lowest order time indicating drum of said time indicating drums;

a transmitting means for transmitting said driving force exerted on said lowest order time indicating drum to upper order time indicating drums in order;

timer mechanism including:

a time setting drum having a side face rotatably fixed on said main shaft,

a cam drum rotatably inside said time setting drum on said main shaft and having a side end formed in cooperative engagement with said side face of said time setting drum,

said cam drum slidably arranged for axial movement toward and away from said time setting drum,

a switch arranged on said frame and operated by the axial movement of said cam drum, and

bias means arranged within said cam drum to bias said cam drum toward said time setting drum;

a second outer shaft rotatably arranged on said main shaft and having one end in engagement with one of said time indicating drums and the other end terminating in a pinion; and

a reduction gear rotatably mounted on said frame to rotate said cam drum at a predetermined rate of reduction and formed with a pinion side adapted to mate with said cam drum and a wheel side adapted to gear with said pinion of said second outer shaft.

2. A digital clock as set forth in claim 1, including a ratchet gear on said time setting drum and a springbiased pawl on said frame in engagement with said ratchet gear.

3. A digital clock as set forth in claim 2, wherein said ratchet gear is provided on the outer periphery of said time setting drum and wherein said spring-biased pawl is arranged around said time setting drum.

4. A digital clock as set forth in claim 3, wherein a spring is disposed in engagement with said time setting drum to apply a resilient force toward said pinion of said second outer shaft to said time setting drum.

5. A digital clock as set forth in claim 4, wherein said cam drum is formed with inner peripheral teeth means thereon for engaging said pinion side of said reduction gear.

6. A digital clock as set forth in claim 2, wherein said time setting drum is provided with a bushing for supporting said time setting drum on said main shaft and wherein said cam drum is loosely arranged on said bushing.

7. A digital clock as set forth in claim 3, wherein said bushing supports said bias means to bias said cam drum toward said time setting drum.

8. A digital clock as set forth in claim '7, including a washer-like retainer fixed on said bushing to maintain said bias means in position.

9. A digital clock as set forth in claim 8, wherein said bias means comprises a spring mounted around said bushing of said time setting drum.

H). A digital clock as set forth in claim 3, wherein said one end of said second outer shaft is fixed to a ten minute time indicating drum.

11. A digital clock as set forth in claim 3, wherein said time setting drum is fixedly secured on said main shaft at one end thereof, and a timer adjusting wheel which is manually engaged is fixedly secured on the other end of said main shaft.

12. A digital clock as set forth in claim 7, wherein said bushing of said time setting drum contacts said pinof said time setting drum to trap said projection at least once in a complete revolution of said cam drum under the influence of said bias means. 

1. A digital clock comprising: a driving source; a frame; a main shaft supported on said frame; a plurality of time indicating drums rotatably mounted on said main shaft for indicating the time; a coupling means for forming an operative connection between said driving source and said time indicating drums and adapted to convey a driving force from said driving source to the lowest order time indicating drum of said time indicating drums; a transmitting means for transmitting said driving force exerted on said lowest order time indicating drum to upper order time indicating drums in order; a timer mechanism including: a time setting drum having a side face rotatably fixed on said main shaft, a cam drum rotatably inside said time setting drum on said main shaft and having a side end formed in cooperative engagement with said side face of said time setting drum, said cam drum slidably arranged for axial movement toward and away from said time setting drum, a switch arranged on said frame and operated by the axial movement of said cam drum, and bias means arranged within said cam drum to bias said cam drum toward said time setting drum; a second outer shaft rotatably arranged on said main shaft and having one end in engagement with one of said time indicating drums and the other end terminating in a pinion; and a reduction gear rotatably mounted on said frame to rotate said cam drum at a predetermined rate of reduction and formed with a pinion side adapted to mate with said cam drum and a wheel side adapted to gear with said pinion of said second outer shaft.
 2. A digital clock as set forth in claim 1, including a ratchet gear on said time setting drum and a spring-biased pawl on said frame in engagement with said ratchet gear.
 3. A digital clock as set forth in claim 2, wherein said ratchet gear is provided on the outer periphery of said time setting drum and wherein said spring-biased pawl is arranged around said time setting drum.
 4. A digital clock as set forth in claim 3, wherein a spring is disposed in engagement with said time setting drum to apply a resilient force toward said pinion of said second outer shaft to said time setting drum.
 5. A digital clock as set forth in claim 4, wherein said cam drum is formed with inner peripheral teeth means thereon for engaging said pinion side of said reduction gear.
 6. A digital clock as set forth in claim 2, wherein said time setting drum is provided with a bushing for supporting said time setting drum on said main shaft and wherein said cam drum is loosely arranged on said bushing.
 7. A digital clock as set forth in claim 3, wherein said bushing supports said bias means to bias said cam drum toward said time setting drum.
 8. A digital clock as set forth in claim 7, including a washer-like retainer fixed on said bushing to maintain said bias means in position.
 9. A digital clock as set forth in claim 8, wherein said bias means comprises a spring mounted around said bushing of said time setting drum.
 10. A digital clock as set forth in claim 3, wherein said one end of said second outer shaft is fixed to a ten minute time indicating drum.
 11. A digital clock as set Forth in claim 3, wherein said time setting drum is fixedly secured on said main shaft at one end thereof, and a timer adjusting wheel which is manually engaged is fixedly secured on the other end of said main shaft.
 12. A digital clock as set forth in claim 7, wherein said bushing of said time setting drum contacts said pinion and rotates independently of the rotation of said pinion.
 13. A digital clock as set forth in claim 12, wherein a projection is formed on said side end of said cam drum and wherein a cut-out is formed on said side face of said time setting drum to trap said projection at least once in a complete revolution of said cam drum under the influence of said bias means. 